A large number of metals are produced from oxide raw materials. Typically, except for oxides of the more noble metals, the metals are produced from the oxides by reduction processes using a reducing agent, such as carbon monoxide, hydrogen, or in some cases other metals, such as aluminum which has a higher thermodynamic affinity for oxygen. Generally, carbon monoxide, and hydrogen are the reducing agents which are of the greatest industrial and economic importance.
Carbon monoxide and hydrogen are usually produced from raw materials such as coal, oil, or natural gas in practice. Dissociation of CO2 and H2O into CO and H2, respectively, requires a large amount of energy for the reaction to be spontaneous, and is considered impractical by industries. At 1300° C., about 160 kJ/mol is thermodynamically required to initiate the dissociation of H2O, while about 147 kJ/mol is required for the spontaneous conversion of CO2. Because of these requirements, waste heat effectively available in typical processes is insufficient to induce the full dissociation, and usually allows conversion of a small fraction of CO2 and H2O to CO and H2. Typical investigations on the utilization of metallurgical slag waste heat have concentrated on thermal energy recovery, direct generation of electricity using thermoelectric principles, and production of fuel gases using endothermic reactions such as reforming of hydrocarbons or decomposition of methanol. See e.g., Barati et al., “Energy recovery from high temperature slags,” Energy 36 (2011); see also Zhang et al., “A review of waste heat recovery technologies towards molten slag in steel industry,” Applied Energy 112 (2013); see also Bisio. “Energy Recovery from Molten Slag and Exploitation of the Recovered Energy,” Energy 22 (1997), among others. It would be advantageous if metallurgical slags could be directly utilized in a system for the dissociation of CO2 and H2O into CO and H2 in order to directly support the reducing agent inventory required for reduction furnace operations with minimal energy loss.
Slag is generally a molten mixture of process waste ashes from the power and metallurgical industries and, at metallurgical plants, are typically tapped from a furnace at high temperatures. Metallurgical slag from steel production typically contains high CaO, while gasification power plants using petcoke carbon feedstock produce V2O3-bearing slags. Typical chemical compositions of metallurgical slags and petcoke ashes are given in TABLE 1. In industry, up to 60 wt. % CaO has been reported in metallurgical slags and up to 74.5 wt. % V2O5 in petcoke ash (note vanadium oxide is present as V2O3 in ash slags from entrained bed gasification. In regions such as China, Eastern Europe, Scandinavia, South Africa, and Russia; where vanadium rich iron ore is processed to produce pig iron; high vanadium oxide content in metallurgical ash/slag is commonly found. In BOF (basic oxygen furnace) slags in Russia, for example, up to 14 wt. % V2O5 can be found. A recent trend of increasing petcoke use as a carbon feedstock in integrated gasification combined cycle (IGCC) power plants has resulted in elevated V2O3 concentration in some of the slags. CaO exhibits a strong thermodynamic affinity for V2O3, resulting in the formation of calcium orthovanadate in a highly exothermic reaction. If CaO-rich metallurgical slags as discharged are appropriately reacted with those from gasification processes using petcoke or other metallurgical processes bearing high vanadium slags, calcium orthovanadate will form, enabling the production of CO and H2 from CO2 and H2O. This disclosure discusses a potential approach to produce fuels from slag waste streams and gas waste streams by blending these industrial slags as tapped from a furnace at a metallurgical plant or at any economically feasible location.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.